This application is related to U.S. application Ser. No. 09/035,982 entitled xe2x80x9cAnti-vibration apparatus and anti-vibration method thereofxe2x80x9d filed on Mar. 6, 1998 and issued as U.S. Pat. No. 6,170,622 on Jan. 9, 2001 naming Shinji Wakui, Takehiko Mayama and Hiroaki Kato as inventors and assigned to the assignee of this application.
The present invention relates to an active anti-vibration apparatus suitably used in a semiconductor manufacturing exposure apparatus or electron microscope which prints a pattern on a reticle onto a semiconductor wafer, or a liquid crystal substrate manufacturing exposure apparatus or electron microscope which prints a pattern on a reticle onto a glass substrate or the like, and an exposure apparatus using the same.
More specifically, the present invention relates to an active anti-vibration apparatus which can suppress an external vibration transmitted to an anti-vibration table and positively cancel a vibration generated by a precision machine itself mounted on the anti-vibration table, and can correct the inclination of the anti-vibration table produced by the moving load of a stage mounted on the anti-vibration table, and an exposure apparatus using this active anti-vibration apparatus.
In an electron microscope using an electron beam, or an exposure apparatus represented by a stepper, a wafer stage is mounted on an anti-vibration apparatus. The anti-vibration apparatus has a function of damping vibrations by a vibration absorbing means such as a pneumatic spring, coil spring, anti-vibration rubber member, and the like.
In a passive anti-vibration apparatus with the vibration absorbing means as described above, although a vibration transmitted to it from a floor or the like can be damped to a certain degree, a vibration produced by a wafer stage itself mounted on the anti-vibration apparatus cannot effectively be damped. In other words, a reaction force produced by high-speed motion of the wafer stage itself vibrates the anti-vibration apparatus to considerably interfere with the positioning settling performance of the wafer stage.
In the passive anti-vibration apparatus, insulation (anti-vibration) of a vibration transmitted to it from the floor or the like and a vibration suppressing (vibration control) performance for a vibration generated by high-speed movement of the wafer stage itself trade off each other.
In order to solve these problems, in recent years, an active anti-vibration apparatus tends to be used. The active anti-vibration apparatus can eliminate the trade-off between anti-vibration and vibration control within a range that can be adjusted by an adjusting mechanism. Above all, when the anti-vibration apparatus adopts feed-forward control, it can realize a performance that cannot be achieved by a passive anti-vibration apparatus.
Not only in the passive anti-vibration apparatus but also in the active anti-vibration apparatus, when the wafer stage mounted on the anti-vibration table performs step and repeat or step and scan operation, the center of its gravity changes due to the movement of the wafer stage to accordingly incline the anti-vibration table. As a sufficiently long period of time elapses, this inclination is naturally corrected and the anti-vibration table is restored to the horizontal state. However, since step and repeat or step and scan operation is performed at a high speed, the position restoring movement of the anti-vibration table cannot catch up with the wafer stage, and the anti-vibration table is consequently inclined.
Although this inclination is a natural physical phenomenon, it incurs a serious disadvantage to an exposure apparatus such as a semiconductor exposure apparatus. For example, a functional unit provided to the main body structure vibrates undesirably due to the inclination of the main body structure, so a predetermined performance cannot be obtained. As a countermeasure for this, a response to the disturbance may be suppressed by increasing the eigenfrequency of the anti-vibration table, i.e., by making the anti-vibration table solid. In this case, however, a vibration of the floor or the like becomes easily transmitted to the anti-vibration table, leading to degradation in anti-vibration characteristics. A technique for correcting the inclination of the main body structure without impairing the anti-vibration characteristics is therefore sought for.
For the sake of further detailed understanding, the above contents will be described with reference to the mechanical arrangement of an active anti-vibration apparatus in which a wafer stage is mounted on an anti-vibration table. FIG. 2 is a perspective view showing an example of the mechanical arrangement of the active anti-vibration apparatus. In FIG. 2, a wafer stage 21 is mounted on an anti-vibration table 22, and active support legs 23-1, 23-2, and 23-3 support the anti-vibration table 22. Each active support leg 23 (23-1, 23-2, or 23-3) incorporates acceleration sensors AC-xx, position sensors PO-xx, pressure sensors PR-xx, servo valves SV-xx, and pneumatic spring actuators AS-xx necessary for controlling the motion in the two axes, i.e., the vertical and horizontal axes. Suffixes xx attached to AC, PO, and the like indicate the directions in the coordinate system in FIG. 2 and the positions of the active support legs 23. For example, Y2 denotes a component incorporated in the active support leg 23-2 located in the Y direction and on the left side.
A phenomenon wherein the Y stage of the wafer stage 21 has moved for a certain distance in the Y direction shown in FIG. 2 and stopped. The movement of the Y stage in the Y direction corresponds to a change in center of gravity of the entire anti-vibration table for the active support leg 23. A thrust which is necessary for maintaining the horizontal posture of the anti-vibration table 22 regardless of the change in center of gravity and should be generated by a vertical actuator in each active support leg 23 is uniquely determined. When the Y stage moves and is set in a steady state, after a lapse of a sufficiently long period of time, because of position control, the active support leg 23 generates a thrust that matches the change in center of gravity, and the anti-vibration table 22 is restored to the horizontal state.
The situation changes when the Y stage continuously performs step and repeat or step and scan operation. As the Y stage moves continuously, the position of the center of gravity also changes continuously. Thus, the active support legs 23 cannot be returned to the preset positions in time, and the anti-vibration table 22 inclines gradually. When the X stage performs step and repeat or step and scan operation, it generates rotation (inclination) about the Y-axis due to the same reason. The inclination of the anti-vibration table 22 degrades the measuring precision of a measuring unit (not shown) or the positioning settling performance of the stage itself, partly impairing the productivity of the semiconductor exposure apparatus. Therefore, a technique for correcting the inclination of the anti-vibration table which is caused by a change in center of gravity upon movement of the stage has been sought for.
In order to solve the above problem, Japanese Patent Laid-Open No. 9-134876 (Anti-Vibration Apparatus and Exposure Apparatus) is known as a prior art. According to this reference, the inclination of an anti-vibration table caused by a change in center of gravity upon movement of a stage is predicted on the basis of an output from the position detecting means (laser interferometer) of the stage, and a feed-forward command value for correcting this inclination is input to the vibration control system of the anti-vibration apparatus. The actuator is a voice coil motor (VCM), to which a steady current for correcting the inclination of the anti-vibration table caused upon movement of the stage is supplied. As is easily understood, drawbacks caused by supplying the steady current are as follows:
(1) The size of a VCM drive power supply becomes large.
(2) The VCM and a power amplifier for driving it generate heat.
(3) A cooling unit for recovering heat generated by the VCM and power amplifier must be provided.
(4) The size of a temperature adjusting unit for the entire semiconductor exposure apparatus becomes large.
Therefore, preferably, a DC current is not supplied to an anti-vibration, vibration-control VCM for a large main body structure such as one in a semiconductor exposure apparatus. A task that requires a large force should be dealt with by a pneumatic spring actuator which can drive a heavy weight by opening/closing a servo valve. In other words, the inclination of the anti-vibration table which is generated by load shift accompanying stage movement is preferably corrected by the pneumatic spring actuator.
Even when a pneumatic spring actuator is employed, the technical issue which arises when moving load correction is to be realized still exists. This is because the characteristics of the pneumatic spring actuator including the servo valve are approximately integral characteristics, that is, an integral of a signal that drives the servo valve is the actually generated driving force.
The present inventors have invented several techniques for correcting the moving load by driving a pneumatic spring actuator.
The first technique provides the arrangement of an apparatus which corrects the inclination of an anti-vibration tale by effectively using pressure feedback disclosed in Japanese Patent Laid-Open No. 10-256141(Active Anti-Vibration Apparatus) and on the basis of the moving position information of the stage, as disclosed in Japanese Patent Laid-Open No. 11-327657 (Active Anti-Vibration Apparatus and Exposure Apparatus).
The second technique does not require pressure feedback as a premise and is disclosed in Japanese Patent Laid-Open No. 11-264444 (Pneumatic Spring Type Anti-Vibration Apparatus). As a premise, this technique requires the driving characteristics of a pneumatic spring to be substantial integral characteristics. According to this technique, a velocity profile as a target value required when driving a moving load such as a stage mounted on an anti-vibration table is feed-forwarded to a preceding stage of a voltage-to-current converter which drives a servo valve for opening/closing the valve of a pneumatic spring actuator. A velocity profile is integrated once by the integral characteristics of the pneumatic spring actuator, and the pneumatic spring actuator generates a driving force corresponding to the position of the moving load. Thus, the inclination of the anti-vibration table is corrected.
In former Japanese Patent Laid-Open No. 11-327657, under the condition that pressure feedback is applied to the pneumatic spring actuator, the pressure is increased or decreased in accordance with a change in moving load, thereby correcting the inclination of the anti-vibration table. However, to apply pressure feedback, a pressure gauge must be indispensably mounted, and the feedback system must be adjusted strictly, leading to an increase in cost.
In latter Japanese Patent Laid-Open No. 11-264444, since pressure feedback need not be applied, moving load correction is easy, which is the characteristic feature. If the characteristics of the pneumatic spring actuator are complete integral characteristics, when a velocity signal is input to the pneumatic spring actuator, a driving force corresponding to the position can be generated. Strictly, however, the characteristics of the pneumatic spring actuator are not integral characteristics, but are pseudo-integral characteristics with a break point within a very low frequency range. Therefore, even when a velocity signal is input to the pneumatic spring actuator with such characteristics, a driving force strictly corresponding to the position of the moving load cannot be generated.
When actually compared to a case without a feed-forward input for moving load correction, with the technique disclosed in Japanese Patent Laid-Open No. 11-264444, the inclination of the anti-vibration table with respect to the moving load remains yet although it can be corrected to a certain degree.
The present invention provides moving load correction which does not require application of pressure feedback as a premise. More specifically, the present invention is to provide an active anti-vibration apparatus in which the effect of correction is improved over the effect of moving load correction achieved by the technique disclosed in Japanese Patent Laid-Open No. 11-264444.
The present invention has been made in view of the above situation, and has as its object to effectively suppress the inclination of an anti-vibration table which occurs when a stage is driven.
The first aspect of the present invention relates to an active anti-vibration apparatus having an anti-vibration table on which a stage is mounted. This anti-vibration apparatus comprises an actuator which supports and drives the anti-vibration table utilizing a fluid, a compensator which generates a signal by PI- or PID-compensating a target value signal concerning the stage and necessary for driving the stage, or a signal equivalent thereto, and a controller which controls the actuator in accordance with an output signal from the compensator. For example, the target value signal (e.g., a target velocity signal) is determined by a profile (e.g., a velocity profile) generated by a profiler.
According to a preferred aspect of the present invention, the compensator can include a PI compensator which PI-compensates a target velocity signal concerning the stage and necessary for driving the stage.
According to another preferred aspect of the present invention, the compensator can include a first P compensator which P-compensates a target velocity signal concerning the stage and necessary for driving the stage, a second P compensator which P-compensates a target position signal concerning the stage and necessary for driving the stage, and an adder which adds output signals from the first and second compensators.
According to still another preferred aspect of the present invention, the compensator can include a PID compensator which PID-compensates a target velocity signal concerning the stage and necessary for driving the stage. Alternatively, the compensator can include a first P compensator which P-compensates a target velocity signal concerning the stage and necessary for driving the stage, a second P compensator which P-compensates a target position signal concerning the stage and necessary for driving the stage, a third P compensator which P-compensates a target acceleration signal concerning the stage and necessary for driving the stage, and an adder which adds output signals from the first, second, and third compensators.
According to still another preferred aspect of the present invention, the actuator includes a pneumatic spring actuator.
According to the first aspect of the present invention, the inclination of the anti-vibration table which occurs when the stage is driven is corrected effectively.
According to the second aspect, the present invention relates to a method of correcting inclination of an anti-vibration table on which a stage is mounted. This method includes the compensating step of generating a signal by PI- or PID-compensating a target value signal concerning the stage and necessary for driving the stage, or a signal equivalent thereto, and the controlling step of controlling the actuator which supports and drives the anti-vibration table utilizing a fluid in accordance with the generated signal.
According to the second aspect of the present invention, the inclination of the anti-vibration table which occurs when the stage is driven is corrected effectively.
The third aspect of the present invention relates to an exposure apparatus having an original stage on which an original is to be placed, and a substrate stage on which a substrate where a pattern of the original is to be transferred is placed. At least one of the original stage and the substrate stage comprises an anti-vibration table on which the stage is mounted, an actuator which supports and drives the anti-vibration table utilizing a fluid, a compensator which generates a signal by PI- or PID-compensating a target value signal concerning the stage and necessary for driving the stage, or a signal equivalent thereto, and a controller which controls the actuator in accordance with an output signal from the compensator.
According to the third aspect of the present invention, the inclination of the anti-vibration table which occurs when the stage is driven is corrected effectively, so a high productivity can be achieved.
The fourth aspect of the present invention relates to a device manufacturing method including the coating step of coating a substrate with a photosensitive material, the exposure step of transferring by an exposure apparatus a pattern of an original to the substrate coated with the photosensitive material, and the developing step of developing the substrate to which the pattern has been transferred. The exposure apparatus has an original stage on which the original is to be placed, and a substrate stage on which the substrate coated with the photosensitive material is to be placed. At least one of the original stage and the substrate stage comprises an anti-vibration table on which the stage is mounted, an actuator which supports and drives the anti-vibration table utilizing a fluid, a compensator which generates a signal by PI- or PID-compensating a target value signal concerning the stage and necessary for driving the stage, or a signal equivalent thereto, and a controller which controls the actuator in accordance with an output signal from the compensator.
According to the fourth aspect of the present invention, the inclination of the anti-vibration table which occurs when the stage is driven is corrected effectively, so a high productivity can be achieved.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.